Reaction of CuX2 (X = NO3, Cl, (SO4)(1/2)) salts and Hpymo . HX (Hpymo = 2-hydroxypyrimidine X = Cl, NO3) in aqueous amine solutions (amine = NH3, CH3NH2) leads to formation of the poorly crystalline three-dimensional open-framework coordination polymer [Cu(pyma-N1,N3)2](infinity) (1). Under the same reaction conditions, but in the presence of amine and group 1 metal salts of single charged voluminous anions, highly crystalline clathrates of the type {[Cu(pymo-N1,N3)(2)]. (AX)(1/3)}(infinity) (1 . AX with A = NH4, CH3NH3, Li, K, Rb; X = ClO4, BF4, PF6) are obtained. The X-ray crystal structure of 1 . NH4ClO4 reveals that the combination of square-planar Cu2+ ion with 120 degrees bond angles provided by Hpymo generates a three-dimensional porous [Cu(pymo-N 1,N3)(2)](infinity) framework with ammonium and perchlorate ions and water molecules included in the pores. 1 possesses a rich host-guest chemistry. Indeed, N; sorption at 77 K by empty host 1 reveals its microporous nature with a BET surface area of ca. 200 m(2) g(-1). Hydrated 1 loses water upon heating and when exposed to moist air regenerates the original hydrated material. Likewise, 1 . NH4ClO4 loses ammonia upon heating, giving the corresponding activated acidic material 1 . HClO4 which upon exposure to gaseous ammonia regenerates 1 . NH4ClO4. In addition, 1 reversibly and selectively sorbs AClO(4) salts (A = NH4, Li, Na, K,'Kb) when exposed to AClO(4) aqueous solutions giving highly crystalline 1 . AClO(4) clathrates. Cl-, NO3-, SiF62-, and SO42- salts are, however, not taken up. Salt sorption curves are of type V and possess hysteresis loops. This behavior agrees with the observed guest-induced structure phase change taking place in the 1 framework after guest inclusion.